Dynamic Class Loading from external Jar

[AndreB]

Hi,

Assume i have a .jar with a simple class "Simple.class" in it.
The jar lies in some directory, e.g. "~/myjar.jar"

I took a looked here,
here and
here.

So i want simply to load any class from this myjar.jar
I dont really have a clue what i am doing wrong. There is always a ClassNotFoundException ...

public static void main(String[] args) throws Exception {
		
		File file = new File(System.getProperty("user.home") + "/myjar.jar");
		
		URLClassLoader clazzLoader = URLClassLoader.newInstance(new URL[]{file.toURI().toURL()});
		
		JarFile jarFile = new JarFile(file);
		Enumeration<JarEntry> entries = jarFile.entries();
		
		while (entries.hasMoreElements()) {
			JarEntry element = entries.nextElement();
			if (element.getName().endsWith(".class")) {
				try {
					Class c = clazzLoader.loadClass(element.getName());
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}
	}

Put any simple jar file in home directory and this code snippet should run.

I my case it generates ClassNotFoundExceptions. What you think ?

[masijade]

Does "element.getName()" return the entire package path?

I.E. a.b.c.hello (without the ".class" extension, of course, but including the entire package "." separated and not "/" separated as defined by the API docs)

Somehow, I don't believe so.

[AndreB]

thanks, you are right.
i didn't read carefully about the "binary name" parameter.

so now i got this working solution

public static void main(String[] args) throws Exception {
		
		File file = new File(System.getProperty("user.home") + "/myjar.jar");
		
		URLClassLoader clazzLoader = URLClassLoader.newInstance(new URL[]{file.toURI().toURL()});
//		System.class.getClassLoader()
		
		JarFile jarFile = new JarFile(file);
		Enumeration<JarEntry> entries = jarFile.entries();
		
		while (entries.hasMoreElements()) {
			JarEntry element = entries.nextElement();
			if (element.getName().endsWith(".class")) {
				try {
					Class c = clazzLoader.loadClass(element.getName().replaceAll(".class", "").replaceAll("/", "."));
					
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}
	}

but is there a better way? How can i acquire a resource as a class ?

[masijade]

Uhm, as soon as you have the urlclassloader simply do

Class.forName(<className>, <classLoader>)